Manual wheelchairs are the primary mode of locomotion for millions of people around the world. Upper limb pain and injury is very common among these manual wheelchair users and can severely impact mobility, independence, and quality of life. The most common types of injury are impingement syndrome of the shoulder and carpal tunnel syndrome of the wrist. Upper limb pain and injury is an emotionally, physically, and financially costly problem.
Wheelchair propulsion is one activity that has been associated with the development of these upper extremity injuries. It is recommended that users reduce how hard they push on the hand rim and to do it less frequently in order to reduce the stresses of propulsion on the upper body.
Power attachment units can mount to manual wheelchairs to assist in propulsion. An example of one such power add-on is disclosed in U.S. Pat. No. 4,759,418, which employs a linkage system that mounts to the wheelchair frame and trails in between the two rear wheels. An electric motor powers a drive wheel that is controlled by a push button located within reach of the user. This type of design, not common to all power attachments, also employs a steering bar that attaches to the front casters in order to guide the wheelchair when being driven by the power add-on. These electric drive attachments are known to be successful in helping to reduce the physical effort needed for propulsion. A drawback is that these types of systems completely eliminate the need for pushing because the user drives the wheelchair, rather than maneuvers it through pushes. In this situation, the user does not benefit from the physical exercise of manual propulsion or the psychological benefits of not being dependent on the device for transportation.
Another example of a power attachment device is push-activated power assist wheels. These combine the benefits of manual push operation by the user and power assistance to reduce the demand on the user's upper extremities during propulsion. Push-activated power assist wheels, similar to those disclosed in U.S. Pat. No. 5,818,189, are battery powered wheels that employ either force or torque sensors, or both, to measure the force applied to the hand rims from the user and amplify that force through the use of motors embedded in the wheels to drive the wheelchair forward or backward. This technology has been shown to have a number of positive effects on wheelchair users, including reduced energy expenditure, reduced push cadence, reduced muscle activation, decreased range of motion, easier hill climbing, increased propulsion speed, and reduced pain during propulsion for those users already experiencing pain. One drawback with this approach, however, is that the employment of force and torque sensors to recognize and quantify the amplitude of the push significantly complicates the design, adding costs and weight. Additionally, because measurements are focused on the hand rim, hazardous situations can be escalated by the assistive power.
Another power assistance system is disclosed in U.S. Patent Application Publication No. 2013/0008732 A1, the entirety of which is incorporated herein by reference. The motion-based push activation power assist system disclosed in U.S. Patent Application Publication No. 2013/0008732 A1 uses motion-based measurements to determine when the user applies a push to the wheelchair hand rims and brakes with the hand rims. The push recognition activates a drive system that provides an assistive driving force to the wheelchair to reduce the demand on the user during propulsion. The brake recognition deactivates the power assist. The provided power assist is proportional to the sensed push and can be modulated to different proportional settings.
A motion assistance system for driving a wheelchair is also disclosed in US Patent Application Publication No. 2014/0262575 A1, the entirety of which is incorporated herein by reference. In certain embodiments of the system disclosed in US Patent Application Publication No. 2014/0262575 A1, a user may control a motion assistance system through a control switch, The control switch may be located on or around the seat or on the push rim of the wheelchair. The control switch may also be a remote control, including for example a wrist remote control that can be worn on the wrist or forearm of a user. The user may thus activate and/or deactivate the motion assistance system by pressing a button, activating a switch, pressing onto a throttle, and the like.
Another assistive driving system for a wheelchair is disclosed in U.S. Patent Application Publication No. 2016/0242977 A1, the entirely of which is incorporated herein by reference. In embodiments of the system disclosed in U.S. Patent Application Publication No. 2016/0242977 A1, an assistive drive force is activated based on the combination of (a) an acceleration of the power assist system (attached to the wheelchair) and (b) a user motion that indicates that the user has applied a manual push to the wheelchair, as detected by a sensor worn by the user. Similarly, an assistive drive force may be deactivated based on the combination of (a) a deceleration of the power assist system and (b) a user motion that indicates that the user has applied a manual brake to the wheelchair, as detected by a sensor worn by the user. Accordingly, embodiments of the assistive driving system disclosed in U.S. Patent Application Publication No. 2016/0242977 A1 protects against the unintended activation and/or deactivation of a power assist system that could result from the use of acceleration and/or deceleration data alone.
Certain aspects of the presently disclosed system provide an improved power assistance system that gives a user an enhanced degree of control over the activation and deactivation of an assistive driving force.